The present invention relates to a linear wavelength dense wavelength multiplexer-demultiplexer, which is an optical component for DWDM (dense wavelength division multiplexing) systems.
An optical communication system comprises three main components: laser sources, optical fibres and detectors. In a DWDM system, different laser sources (i.e. sources operating at different frequencies) are used, and the signal of each source is coupled into a single optical fibre in order to increase the transmission capacity. Devices for coupling in and coupling out are known as multiplexers and demultiplexers. The role of the multiplexer is to simultaneously combine the signal from each laser source into the optical fibre. The role of the demultiplexer is to separate the different wavelengths from the optical fibre to different output fibres, the number of output fibres being equal to the number of wavelengths present.
Typically, multiplexers and demultiplexers use diffraction gratings to combine and separate the signal components in the optical fibres. However, the equally spectrally spaced wavelengths are not equally spaced physically after the reflection on the grating. Consequently, some manufacturers have developed proprietary adapters where the input or output fibres are not linearly spaced, in order to account for the non-linearity of the reflected wavelengths. These proprietary adapters are quite expensive.
This poses particular problems, since fibre ribbon connectors, in which the output or input fibres are physically equally spaced, are used more often and are cheaper than the proprietary adapters.
There is thus a need for a device which matches the relation between the spectral separation and the physical separation of each wavelength when coupling in or coupling out frequencies in a MUX/DEMUX.
It is an object of the present invention to provide a linear wavelength DWDM device which corrects the relation between the spectral separation and the physical separation of each wavelength.
In accordance with the invention, this object is achieved with a linear wavelength DWDM comprising: a generally rectangular-shaped optically transmissive medium having a constant index of refraction, two opposite ends, two opposite sides and a thickness. The linear wavelength DWDM is provided with a first and second port, each of defining an optical axis. The first port is adapted to receive an optical fibre, and the second port is adapted to receive an optical fibre ribbon comprising a plurality of optical fibres which are physically equally spaced along a line. The first and second ports are in optical communication with each other through a combination of a first mirror, a second mirror and a diffraction grating, the first and second mirrors and the diffraction grating defining an optical path between said first and second ports within said device. The diffraction grating is preferably at an angle xcex8, and at least one of the first and second mirrors respect an f-sin(xcex8) condition, in order to provide a correction for the non-linear relationship between the spectral spacing between the different wavelengths and the physical spacing thereof.